This invention is primarily intended for use with power generators such as those used with Recreational Vehicles (RVs), including motor homes, coaches, campers, trailers, fifth-wheel trailers, and boats. It is not intended to be limited to those applications, and should be understood to be applicable to other arrangements in which power generators are used.
To understand the unique and valuable aspects of this invention it is useful to understand the typical power system found on Recreational Vehicles (RVs), boats, emergency vehicles, and stationary energy systems that incorporate engine driven diesel, gas, liquefied petroleum, or other generators. These systems frequently have intermittent AC power needs and multiple sources of power available. Often the critical systems are supplied by a DC battery system and the non-critical loads are supplied by the AC system.
RVs for example have both a 12V DC house or domestic system and a 120V AC system. The DC system commonly provides power for area lighting, stereo, water pumping, and other loads requiring relatively small amounts of power. The 120V AC system powers larger loads such as the microwave ovens, hot water heaters, heating and air conditioning (HVAC), and convenience outlets that supply power to loads such as entertainment systems. The domestic refrigerator is commonly supplied by both the 12V DC system and the 120V AC system, and sometimes alternatively by propane. Some systems also include a 12V DC to 120V AC inverter. Often the RV (or boat or other power user) is able to operate with only the DC system but the AC system provides additional comfort and features.
RVs and boats have similar systems and both typically have a power inlet for park power or shore power, as these industries refer to the AC utility power grid. These power inlets are commonly either 30 A 120V single phase AC or 50 A 120/240V single phase AC. Thus there are frequently two or three AC power sources available. Power transfer relays are commonly configured so that the priority of the power sources is:
Utility or Shore Power
Genset (generator)
Inverter
Typically the inverter only supplies AC devices that are the highest priority, such as the microwave, entertainment, and convenience outlets. It is not practical to run loads like hot water heaters and HVAC systems from inverters that are ultimately powered from batteries. Frequently the total AC power requirement of all of the system loads exceeds the park/shore power inlet, and consequently requires running the genset to power the entire system.
The operators of RVs must constantly monitor these various systems and make decisions about which power source to use and when. This results in less than optimal operating efficiency and great inconvenience. For example consider the RV camping situation in which there is no AC power. The DC system is used for lighting, refrigeration, and other applications. Perhaps there is also an inverter. Eventually the battery will become discharged under such constant use. The operator must monitor the battery and decide when to start the generator to recharge the battery and then continue to monitor it until it is charged and then stop the generator. Loads like HVAC systems which have intermittent on/off duty cycles require the operator to choose either to let the generator to run continuously or to repeatedly manually stop and start the genset.
Current systems for monitoring and controlling generators are generally lacking. In U.S. Pat. No. 1,507,300 Replogle teaches starting and stopping an internal combustion engine-driven generator based on battery voltage. Today there are a number of commercially available systems that will initiate starting and stopping the generator based on fixed voltage points. But the use of a single voltage point for starting and stopping requires considerable compromise because the state-of-charge of the battery is difficult to assess from the instantaneous voltage. Additionally many of the commercially available systems impose fixed minimum run times which can lead to excessive genset running.
The general notion of starting and stopping the genset based on demand from HVAC systems is taught by Picklesimer in U.S. Pat. No. 4,788,487. The Picklesimer system controls both starting and stopping of the genset and includes transfer relays for sequentially loading the genset after a fixed time delay from starting the genset. A fixed time is also imposed after the HVAC demand has been satisfied for genset cool down. As Picklesimer explains, “ . . . the invention will permit continued repetition of the start up and shut down procedures as described to permit the interior of the motor home to be held to a narrow thermostat temperature range setting . . . ” Though seemingly better then previous systems, the resultant “short-cycling” of repeated starting and stopping the genset causes excessive wear on the engine starting system. If the on demand time is relatively high it is actually better for the genset to run continuously.
Commercially available automatic starting systems suffer from the shortcomings described above as well as a lack of sufficient inputs and outputs to allow comprehensive control of the RV power system. The manufacturers of inverters have incorporated automatically starting and stopping the genset as part of the inverter system. It typically requires the purchase of a specific expensive model of inverter as well the optional monitoring panel (for example, a Trace RV series with RC-7G). Even so it does not include servicing run requests from HVAC systems. Some stand alone generator starting systems (for example, Heart AGS) have attempted to integrate automatic genset starting using both HVAC run requests and battery voltage. By imposing a minimum run time of 2 hours the unit effectively causes continuous genset running. Additionally none of the existing units interface well to the genset. No genset fault or error messages are displayed, the genset battery is not monitored, and typically the genset cannot even be conveniently started and stopped manually from the user interface.
The user interface supplied by most genset manufactures is very simple. Onan a Cummins Inc, subsidiary, has a remote that consists of an ON-OFF-ON rocker switch with a back-light and an hour meter or an analog volt meter. The back-light in the rocker switch is use to annunciate genset faults. Two levels of faults exist. For the first level the light is flashed about once per second if the engine temperature is high, it will flash about twice per second if the oil pressure is low, and if the light flashes about three times per second the user may hold the stop switch down for one to five seconds to access a second level of diagnostics. The light flash sequence now contains two digits corresponding to an error message. For example if the fault code were 38 there would be a sequence of three flashes followed by eight more that would lead the user to a table of error codes for the message: Over current low power factor loads, reduce load. Users are likely to be confused and unsuccessful when decoding this type of information. Additionally genset faults are only annunciated for five minutes, which means the user could have a fault but not know it. When the system is automated this is an issue as more elements are involved in the start/stop process.
Safety should be prime concern when automating the starting and stopping of the genset in a RV. Many RV owners have garages, buildings, or sheds where they park their RV. If there is a possibility of carbon-monoxide poisoning or suffocation from exhaust gasses automatic genset starting should be prohibited. Systems that are currently available have not adequately addressed the safety problems. The Heart AGS for example, recommends turning it off when the coach is in motion. This means it cannot be used in the automatic mode while traveling, even though this would be desirable for most motor homes.
The integration of genset user interface, system monitoring, and automatic control has substantially lagged monitoring and control systems of inverters. Inverter manufactures have also generally failed to integrate genset monitoring and control. Presently the typical RV may have a monitoring and control panel for the inverter, for the genset starting system, and for manual control and limited fault annunciation, perhaps with a mechanical hour meter or an analog voltmeter. The components of the system inappropriately overlap, have missing control features, tend to be costly, and nonintuitive. For the typical RV user the systems need to be simple to use with functionality appropriately divided.
Current systems reveal a lack of integration of key system elements, a lack of a user interface that is intuitive and informative, and a lack of safety features to protect users. They also rely on single point fixed times and voltage for control, potentially resulting in excessive running or excessive starts and stops. Thus there is a need for an improved system that addresses one or more of these shortcomings and advances the art with several significant new innovations.